U.S. Pat. No. 6,113,874 discloses heat recovery methods useful with furnaces employing regenerators wherein a stream of combustion products formed in the furnace is passed through a first regenerator to heat the first regenerator and cool the combustion products, and then a portion of the cooled combustion products is combined with fuel to form a mixture which is passed through a second heated regenerator wherein the mixture undergoes an endothermic reaction to form syngas that then passes into the furnace and is combusted.
This patent mentions that some of the combustion products (“flue gas”) can be passed from the furnace through a separate regenerator to heat this separate regenerator, following which technically pure oxygen can be passed through this heated separate regenerator to heat the oxygen which is then fed from the regenerator into the furnace for combustion.
However, what is said in this patent to be the “optimal” amount of combustion products from combustion of syngas made from a mixture of pure CH4 and recycled flue gas and pure O2 as oxidant to be passed from the furnace into this separate regenerator, relative to the amount of the combustion products to be passed from the furnace into the first or second regenerators that are used to provide heat for the endothermic reaction to form syngas, has been discovered by the present inventor to be not at all optimal in terms of improving the overall efficiency of the operation. Indeed, the present inventor has found that significantly improved efficiency and energy utilization are available by utilizing conditions that are not taught or suggested by what this patent discloses about apportioning the flows of combustion products to the separate regenerator relative to the flows to the first and second regenerators. Indeed, the present inventor has determined a superior basis for apportioning the flows of combustion products to the separate regenerator relative to the flows to the first and second regenerators, and has found what is the optimal apportionment of these flows of combustion products. Furthermore, the present inventor has found a preferred method to apportion the flows of combustion products to the regenerators relative to the flows to the first and second regenerators for different amounts of recycled flue gas mixed with the reforming fuel.